Email told fatal shuttle it was safe

The seven Columbia astronauts killed when the shuttle tumbled out of control on its return to earth on February 1 had been assured that there was no cause to fear that the foam that had struck the spacecraft on takeoff might endanger its safe return.

Flight director Steve Stich gave the assurance to Columbia's commander and pilot on January 23, according to documents disclosed yesterday. But at the same time Nasa engineers continued to consider whether the foam might have fatally damaged material protecting the shuttle during its descent.

"Experts have reviewed the high speed photography and there is no concern for RCC [reinforced carbon carbon] or tile damage," Mr Stich wrote in an email to the commander, Rick Husband, and the pilot, William McCool.

"We have seen the same phenomenon on several other flights and there is absolutely no concern for entry."

Husband, a veteran shuttle astronaut, replied two days later: "Thanks a million, Steve!"

Investigators are increasingly convinced that a chunk of foam from the external tank smashed against Columbia's left wing, loosening a protective panel along the leading edge. That could have let searing temperatures penetrate and melt key structures untilColumbia tumbled out of control at nearly 13,000 mph.